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    STP1480

    Effect of Microstructure on Pit-to-Crack Transition of 7075-T6 Aluminum Alloy

    Published: 01 January 2007


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    Abstract

    The focus of this research was to gain an increased understanding of how microstructure influences pit growth, pit-to-crack transition, and critical crack propagation to fracture. Two thicknesses of 7075-T6 aluminum alloy were etched and subjected to corrosion fatigue in a 3.5 % sodium chloride environment. 7075-T6 aluminum alloy is of particular interest to the aging aircraft community, as this alloy has been used extensively on wing and fuselage structures for both military and commercial aircraft in the past. Testing was interrupted at various intervals to obtain information on pit generation, growth, and potential cracking. Results indicated that microstructure has a significant influence on pit-to-crack transition and fatigue crack propagation. Short cracks (< 100 μm) in a corrosion fatigue environment were strongly influenced by grain boundaries and crystallographic grain orientation. Constituent particles competed with corrosion pits as critical crack nucleation sites. Post-fracture analysis confirmed the presence of noncritical cracks within the corroded region, related to pitting and constituent particles.

    Keywords:

    aluminum, corrosion fatigue, pitting corrosion, SEM


    Author Information:

    Jones, Kimberli
    Research Assistant Engineer and Professor, University of Utah, Salt Lake City, UT

    Hoeppner, David W.
    Research Assistant Engineer and Professor, University of Utah, Salt Lake City, UT


    Committee/Subcommittee: E08.09

    DOI: 10.1520/STP45519S